Ain't singing for Pepsi,

Ain't singing for Coke,

I don't sing for nobody

Who makes me look like a joke.

So rocker Neil Young proclaims in his song This Note's For You. The reality is rarely so simple. Big concerts are hugely expensive to stage, but they also provide a chance for bands, promoters, merchandisers, sponsors, and assorted hangers-on to make a lot of money.

A ticket to see a band play in the Point Depot or the RDS will normally cost between £20 and £30. But many concert-goers will be persuaded to part with a whole lot more of their cash before the night is out. Before you even reach the venue, you can expect to pass an array of ticket touts and other sellers who congregate on the streets outside. Here, you have the chance to pick up a cheap T-shirt or poster. Prices are low because the illegal traders don't bother with tax or licensing fees - they just take the money and run.

Once you get inside the venue, the marketing goes into overdrive - stands selling every conceivable form of merchandise relating to the band, from key-rings to T-shirts, and nothing comes cheap. Prices are high because everyone wants a cut: the seller, the band, the venue and the taxman.

Dave Bell of Irish Merchandising Services and Seminal Merchandising organises merchandising in the Point and at many other venues. He claims Boyzone sell more merchandise than any other pop band. The goods produced are carefully targeted:

"When Boyzone started out, it was very much a kiddie audience and we produced lots of trinkets - whistles, necklaces, key-chains. Now as the band's audience has got older they're more fashion-conscious, so we sell really nice garments - jackets, hooded-fleece tops. "That's purely because the audience is ageing and has more disposable income." Mobile phone bags with the Boyzone logo are another of the more recent successes.

Rock audiences are older and may not spend as freely, but they're still worth a lot of money to merchandisers. Bell says a Boyzone audience might spend an average £5 a head on merchandise, while the audience for an indie band such as Radiohead might spend £2.50 a head. However, the sales record for the Point was broken last year by the heavy metal band Metallica, whose fans paid out an enormous £7.50 a head (the Point has a capacity of between 8,000 and 8,500, so that's £60,000-plus of merchandise in one evening).

So you've bought yourself a T-shirt, a key-ring and a couple of glow-sticks. A lot poorer, but still happy, you decide to get a drink, or maybe some chocolate. If you look around the foyer in the Point, you'll find that certain brands are prominently displayed and have huge stalls all to themselves. These are what the Point's general manager, Cormac Rennick, describes as the "preferred suppliers" - Coca-Cola, Guinness, Mars and Marlboro cigarettes. They pay for the privilege of having those stalls, and they're guaranteed lots of business.

One Coke and one Mars later, you head into the auditorium, leaving all that commercialism behind you. Well - not quite.

Look around the auditorium and you'll see the walls and balconies draped with the names of media sponsors - everything from The Irish Times or the Evening Herald to 2 FM or Today FM. Some of these are arranged as "contra deals" with the promoter, i.e. no money changes hands. The newspaper or radio station agrees to carry advertisements for the concert and, in return, gets its name on the tickets, on the ads and at the venue.

There may also be banners for a corporate sponsor. Often, the really big acts will secure a world sponsor when they go on tour, to help cover expenses - Cher had the backing of the Internet company America Online for her tour last year. In the past, Volkswagen has sponsored Bon Jovi, and Rover have sponsored Brian Adams. Perhaps the most famous deal of all came in the 1980s, between Michael Jackson and Pepsi. This multi-million dollar deal showed just how eager a big company was to associate itself with a pop star. (According to Jackson's biographer, J. Randy Taraborrelli, the singer is a health-food fanatic and certainly not a fan of sugary soft drinks.)

Justin Green of concert promoters MCD predicts more and more Irish sponsors will get involved with big concerts. "Over the last 10 years, the interest from companies has trebled. Companies are becoming aware that people are bombarded with advertising through the normal routes. They say that between going to work and coming home you see something like 320 advertisements a day. Companies are choosing different routes to reach their target markets."

You're in the auditorium, waiting for the show to start. First, it's the support acts. Pop bands now often have three and four support acts in a row, each a group of young hopefuls getting to play to a captive audience. These bands do a hard-sell, pushing their debut single or album in between hollers of "Hello Dublin!" and "Does Dublin wanna partaaaaay?!"

Almost all major concerts now make use of big screens, which are there so you can see close-ups of the band - and which are a great help if your seat is a long way from the stage. However, promoters have in recent years started using the screens for "entertainment packages" (see below). In the case of Boyzone and Steps, who played the Point last December, this meant lots of footage of George Clooney, Leonardo DiCaprio, Michael Owen and all the other heart-throbs guaranteed to get young girls shrieking. Mixed in with this were ads for deodorant, perfumes and the Disney Channel.

So it may be several hours before the band you paid in to see eventually takes to the stage. By which time you may feel a longing for another Coke and a Mars - if you've any cash left.